A method was previously developed in this Laboratory for estimating the enzyme renin in rabbit plasma (Lever, Robertson & Tree, 1963 a, b,c, 1964. The present paper describes the adaptation of the method to the measurement of renin in the plasma of man. Preliminary accounts of this work have been published (Brown, Davies, Lever & Robertson, 1963a, b, 1964a. METHODSThe technique consists of an estimation of renin concentration by determining the initial velocity of angiotensin formation under standard conditions of incubation with substrate. Angiotensinase-free ox-serum substrate, as prepared for the estimation of rabbit renin (Lever et al. 1964), was used throughout the present studies. The technique of incubation and assay, and the tests for contamination with angiotensinase and endogenous substrate, were also as described by Lever et al. (1964). The methods of preparation of standard human renin, and of extracting renin from human plasma, however, differed from those used with the rabbit.Preparation of standard human renin. Human kidneys (4.5 kg.) were obtained poet mortem, and excess of fat and fibrous tissue was removed. The kidneys were then minced and allowed to stand in 101. of water at 8°for 36 hr. The mince was filtered through muslin, and 10% (w/v) trichloroacetic acid was added to the filtrate at 80, with constant stirring, to give pH 2-9. Then NaCl (52 g. to each litre) was added slowly with stirring; the pH was checked after 15 min., and if necessary readjusted to pH 2-9 by adding 10% trichloroacetic acid or N-NaOH. The solution was then filtered at 80 overnight through Whatman no. 50 paper and the filtrate adjusted to pH 5-0 with N-NaOH. Then 2 1. batches of this solution were dialysed in Visking cellophan sacs (28/32 in.) against three 15 1. changes of water at 80 over 48 hr. (unpublished work) during the purification of pig renin. The 2 1. batches of renin solution were dialysed in Visking cellophan sacs (28/32 in.) against three 151. changes of 5 mM-sodium phosphate buffer, pH 7 0 (0-0240% NaH2PO4; 0-1074% Na2HPO4,2H20), over 48 hr. at 80. This solution was then applied at room temperature to a column (65 cm. x 2-5 cm.; dry wt. 100 g.) of lightly-packed DEAE-cellulose equilibrated with the 5 mM-sodium phosphate buffer, pH 7-0. Renin was adsorbed during this application. The column was washed with 31. of 0 03M-sodium phosphate buffer, pH 7*0 (0-140% NaH2PO4; 0-653% Na2HPO4,12H20), and the eluted protein discarded. Renin was then eluted with 600 ml. of 0 35M-phosphate-saline buffer, pH 6.0 (0-05M-Na2HPO4; 0 3M-NaCl, adjusted to pH 6-0 with 6N-HCI), containing neomycin sulphate (0-01 %).The eluate was dialysed against three 101. changes of glycine-HCl-saline buffer, pH 3-0 (0 IM-glycine; 0-9M-NaCl; 0 018N-HCI), at room temperature over 24 hr. The precipitate that then formed was removed by filtration

The mechanisms controlling the secretion of aldosterone are incompletely understood

1. Exchangeable sodium (NaE), plasma electrolytes and arterial pressure were measured in 121 normal subjects and 91 patients with untreated essential hypertension (diastolic greater than 100 mmHg), 21 of whom had low-renin hypertension. Plasma concentrations of renin, angiotensin II and aldosterone were measured in all hypertensive patients, total body sodium, total body potassium and exchangeable potassium (KE) in some patients. 2. Mean NaE was not different in normal and hypertensive subjects provided the two groups were matched for leanness index. In the subgroup of young hypertensive patients aged 35 years or less mean NaE was below normal. NaE was not related to arterial pressure in normal subjects but in hypertensive patients there were positive and significant correlations of arterial pressure with NaE and with total body sodium. 3. NaE and total body sodium increased with age in hypertensive but not in normal subjects. Partial regression analysis suggested that the correlation of NaE with arterial pressure was not explained by an influence of age. 4. Mean NaE was not increased and mean KE was not decreased in patients with low-renin hypertension. 5. Plasma potassium concentration, KE and total body potassium correlated inversely and significantly with blood pressure in hypertensive patients. These correlations were more marked in young than in old patients. 6. Multiple regression analysis showed that the combination of NaE and plasma potassium concentration 'explained' more of the variation of systolic blood pressure in hypertensive patients than it did in normal subjects. Plasma potassium concentration 'explained' more of the variation in young hypertensives and NaE 'explained' more in older patients. 7. Our findings suggest than changes of plasma and body potassium are important in the earlier stages of essential hypertension and that changes of body sodium become important later.

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